Cushion drill collar



June 6, 1967 c. H. LEATHERS ETAL 3,323,327

CUSHION DRILL COLLAR Filed May 20. 1965 Mg gal nited States Patent O 3,323,327 CUSHION DRILL COLLAR Clarence H. Leathers, Redondo Beach, and Jeddy D.

Nixon, San Pedro, Calif., assignors to Grant Oil Tool Company, Los Angeles, Calif., a corporation of California Filed May 20, 1965, Ser. No. 457,328 6 Claims. (Cl. 64-23) This invention relates to well drilling equipment and more particularly to a drill string shock absorber for use in a rotary well drilling string.

In the rotary method of well drilling it has become common practice to employ a drill collar section above the Ibit with drill pipe extending upward from the drill. collar section. The drill collar section supplies as much weight as possible directly above the bit, such that the compressive force necessary on the bit is exerted by the drill collar section while the drill pipe portion of the string remains in tension. However, a rotary drill 'bit in meeting various earth strata continuously subjects the drill string to shock and vibration. The drill collar removes much of the vibrational and shock forces but a substantial amount of vibration is still transmitted from the bit on the bottom of the hole upward through the drill string under various circumstances. This is especially true when resonance is included which can cause severe vibration even above the rotary table.

The present invention provides an improved drill string shock absorber for the absorption of vibrational and shock forces from the bit so that they will not be relayed through the drill string. Prior art drill string shock absorbers have been constructedy to allow a relatively large movement vertically in the material which is employed to damp the shock and vibration forces. That is, prior art devices such as that described in copending application Ser. No. 314,251, filed Oct. 7, 1963, now Patent No. 3,225,566 by Clarence H. Leathers entitled, Drill String Shock Absorber, assigned to the assignee of the present application utilize a compressible fluid in a closed chamber positioned between a mandrel and body portion of the shock absorber.

The chamber of compressible material is formed such that the parts of the shock absorber are separated vertically by the compressible material and. all vertical force transmission is through the material. In such prior art devices relative vertical travel between the parts due to the compressibility of the material has been substantial and the amount of movement allowed causes problems in the construction and operation of the device. Prior to the lpresent invention relatively large movement was provided to damp out vibrations and forces, as more fully discussed hereinafter,

It is an object of the present invention to provide an improved drill string shock absorber or cushion drill collar which is of simplified and more ellicient construction.

Another object of the present invention is to provide an improved cushion drill collar which obviates the problems of sealing a uid chamber and sealing against movement of two relatively moving portions of the device.

A primary object of the present invention is to provide an improved cushion drill collar which prevents the transmission of high frequency vibration forces upward through the drill string.

Another object of the present invention is to provide an improved cushion drill collar which requires no special drilling procedure or maintenance for its operation.

Another object of the present invention is to provide an improved drill `string shock absorber which is eicient and has a longer useful life than shock absorbers heretofore known to the art.

ice

The cushion drill collar of the present invention comprises a body portion and a mandrel portion vertically separated by a body of plastic through which vertical forces are transmitted.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof will be better understood from the following description description considered in connection with the accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

In the drawing:

FIGURE 1 is a fragmentary vertical sectional view through the earth showing a device installed in a drill string within a well and- Showing the preferred relationship of the installed device with the drill bit;

FIGURE 2a and 2b are enlarged partially sectional views in elevation of the presently preferred embodiment of the device of the present invention; and,

FIGURE 3 is a Sectional view taken along line 3 3 of FIGURE 2.

As briefly discussed above, prior art drill st-ring shock absorbers, sometimes referred to as cushion drill collars, have been constructed to allow a relatively large vertical movement between the parts of the device above and below the isolating material. For example, referring now to the drawing, there is shown in FIGURE l a typical mode of operation of a shock absorber in a drill string. The shock absorber lll is shown disposed between a drill collar section 12 -of the drill string 14 and the usual rotary bit 16 in a well 18. The drill collar 12 is of sufficient Weight to provide the necessary compressive force on the bit 16 during drilling operations. The drill collar of the drilling string is typically one or more sections of steel tubing ten feet or more in length. The drill collar is provided with a fluid conducting bore but is of considerably greater wall thickness than the drill pipe. Thus, a drill collar provides additional weight and rigidity in the drilling assembly immediately above the drilling tool. As an illustration, such a drill collar section, in 12% inch hole, for example, typically may weigh on the order of 100,000 pounds and it is primarily this weight that is exerted on the bit at the bottom of the hole during drilling operations. The drill string 14 is supported under tension in the usual manner by suspension from a rotary table 20 above the surface 22 of the earth.

In prior art devices the amount of vertical movement of the drill bit relative to the drill collars above the shock absorber due to the compressibility of the isolating material under a typical load of 100,00() pounds is typically 1 to 6 inches. The compressibility of the material to allow damping of movement up to approximately 6 inches was t-o accomplish this isolation. The present invention provides a device which isolates the shock load and vibrations but has no parts which move relative to one another in such manner as to require sealing. For example, in prior art devices such as that shown in application Ser. No. 314,251 supra, in order to retain the isolating fluid, a closed chamber is defined between vertical walls of the mandrel and body portions of the device. In order to maintain the fluid integrity of the chamber it is necessary to seal between the mandrel wall and body wall where the relative vertical movement occurs. Such movement of parts under the loading and environmental conditions that exist in the well make the sealing problematical both in construction of the device and maintenance.

In FIGURES 2a and 2b, there is shown a presently preferred embodiment of the shock absorber of the present invention which comprises in general a body A and a mandrel B telescopically matable therein for axial movement relative one to the other. The body A is of elongate cylindrical configuration having an outside surface 28 of substantially constant diameter approximately equal to the outside diameter of the dril-l collar l2 and substantially less than the diameter IS of the well being drilled. At the upper end of the body A there is provided a malethreaded connecting end 24 of the conventional type for connection to the lower end of the adjacent drill collar or drill string component. Although the body A can be formed as an integral unit, for ease of manufacture it is constructed by division into an upper portion 26 and a lower portion 30 in the presently preferred embodiment. The upper portion 26 and the lower portion 30 are threadably engaged by mating threads 25. The body A defines by its internal surface 32 an upper cylindrical bore 33 and by its lower internal surface 4i a lower cylindrical bore 42. Although intermediate diameters to accommodate thread formation and assembly may be necessary the cylindrical bores 3S and 42 are those that determine the operation of the device as will lbecome more apparent hereinafter. The upper cylindrical bore extends from the upper end of the body in communication with the bore through the drill collars and remainder of the drill string for circulation of drilling uid. The lower cylindrical bore 42 defined by the wall 4l is of substantially greater inside diameter, being limited only by the necessary wall thickness of the body at that portion defining the lower cylindrical bore 42. The lower cylindrical bore 42 extends from a point proximate the upper end of the lower portion 34? of the body to the lower end 44 thereof. Thus, the lower end of the body is open with an inside wall extendinfy upwardly to a point just below the connection of the lower portion 3u of the body to the upper portion 26 thereof. The cylindrical bore 42 terminates at an inwardly extending transverse shoulder 43 defined by the internal surface of the body at the upper end of the bore 42. Illustrative of the relative diameters, in a typical embodiment of a shock absorber of one size the bore 38 dened by upper cylinder wall 32 is approximately three inches in diameter while the lower cylinder 42 is approximately eight inches in inside diameter. A region of decreased wall thickness and spline grooves are provided in the body extending upwardly from the lower end as described hereinafter.

Through the wall of the body there are provided a series of longitudinally spaced openings or ports 46 closed by removable plugs 48 for inserting a retaining and travel limiting member 49 into the shock absorber as discussed hereinafter.

Removal of the retaining member 49 allows assembly of the mandrel B into the body and the retainer 49 when positioned in the annular groove 52 of the mandrel prevents disassembly and furnishes a stop surface 56 to limit the downward movement of the mandrel in the body as will become apparent hereinafter.

The mandrel B as shown in FIGURE 2 is an elongate member having a bore S8 of substantially constant inside diameter extending throughout the length of the mandrel, which bore is co-extensive with the bore 38 through the drill string when the mandrel is assembled within the body as shown in FIGURE 2. The mandrel is adapted to be longitudinally matable within the body portion of the shock absorber. The mandrel is constructed as described hereinafter to provide an upper portion matable with the bore 42 of the body and a lower end 66 to which the drill bit or other component of the drill string is attached. The portion 64 of the mandrel which is matable with the body and is referred to hereinafter as the mating section has an Outside diameter substantially equal to but less than the inside diameter of the bore 42 of the body A and is adapted to be slidably movable with respect thereto. The mandrel is so constructed and arranged that a longitudinal portion thereof is formed `of dimensionally stable resilient compressible or deformable material which is capable of shortening in its vertical dimension under the loads encountered due to shock and vibration while having sufficient strength in compression to transmit the normal loads therethrough. In the presently preferred embodiment Delrin acetal resin, a tradename of Dupont Chemical Company for polymerized formaldehyde.

The upper end of the mandrel defines a horizontal shoulder 54 engageable with the horizontal shoulder 43 of the body through which the vertical forces from and into the body are transmitted. The upper end section 44 of the mandrel in this embodiment is thus of two diameters the smaller of which is above the mandrel shoulder 54, in the orientation of the figures and the lower of which is greater and matable with the bore 42 of the body. It will be seen that the upper end section 44 of the mandrel can take various forms so long as it transversely engages the body as at the bearing Contact between the shoulders 43 and 54. In the downwardly facing annular surface 57 of the end section 44 an indentation is defined into which the upper end 59 of the tubular isolating member 60 is inserted. The isolating member is tubular in form with an inside diameter coextensive with the bore 58 through the mandrel. The outer diameter of the isolating member is approximately equal to but less than the outside diameter of the mating section 64 of the mandrel. The outside diameter of the compressible member is sufficiently less than the bore 42 of the body to allow deformation of the member for the necessary compressibility. As an illustration of the relative size of the member to achieve necessary vibration isolation the length of the member 60 in this embodiment is approximately 30 inches.

The lower end of the compressible member 60 is engaged with the upper end 62 of the lower segment 65 of the mating section 64. Thus, the mating section 64 of the mandrel is formed in three segments; the upper end section 44, the intermediate isolating member 60 and the lower segment 65. Therefore, the metallic mandrel is interrupted along its length by a length of compressible plastic and all forces passing from the drill string downward to the bit or from the bit upward to the drill string must be transmitted through the plastic compressible member. It has been found in accordance with the present invention that the compressibility of the plastic member 60 due to its longitudinal deformation prevents the transmission of high frequency shock and vibration and prevents such vibration from becoming resonant in the drill string. As shown in FIGURES 2b and 3, proximate the upper end of the lower portion 66 of the mandrel there are provided a series of circumferentially spaced longitudinally extending grooves 74 in the outer surface thereof. At a corresponding longitudinal position along the cylinder wall 34 of the body A there is provided an inwardly extending annular protrusion 76 in which circumferentially spaced longitudinally extending grooves 78 are formed. The grooves 78 in the internal Wall of the body are spaced in matable relationship with the grooves '74 in the mandrel such that splines 80 can be inserted therein is shown in FIGURES 2b and 3, to prevent rotational movement therebetween. These splines are thus drive splines which cause the mandrel to be rotated when the body is rotated.

Bet-Ween the outer surface of the mandrel portion 64 and the internal wall 34 of the body portion 30 there is provided a sealing member 82 extending circumferentially around the mandrel. O-ring seals are provided at 83, 84 and 85 for sealing between the upper end portion of the mandrel and mating surface of the bodies and between the isolating member 60 and the -adjacent surfaces of the upper end portion and lower segment of the mandrel. Sealing of the circulating bore 38-58 of the device from the mating surfaces is essential. The fluid pressure of the circulating uid would erode and wash out the tool if the fluid were allowed to ow through the Spaces between the mandrel and mating portions of the body.

The -annular groove 52 into which the retention balls 49 are engaged to retain the body and mandrel in assembled condition are longitudinally extended to allow for foreshortening of the device after operation and wear. It can be seen that in assembled condition the mandrel is fixedly retained -against longitudinal movement in the body by the shoulder 53 and the retention members 49. Accordingly, in operation with a drill bit attached to the lower end of the mandrel as shown in FIGURE l, the weight of the drill string above the cushion drill collar of this invention is transmitted through the body A downwardly through the downwardly facing shoulder 43 to the mandrel upper end segment 44 and thus through the isolating member 60 to the lower segment 65 of the mandrel to the bit. Conversely, forces acting upwardly on the bit and mandrel are transmitted upward through the isolating member 60, the shoulder S4 and up the drill string. The mandrel below the isolating member 60 is free to move upwardly by the amount by which the isolating member is compressed since the groove 52 into which the retention members fit allows longitudinal movement of the mandrel upwardly as shown by the dotted lines in FIGURE 2a. As can be seen, however, during such operation bearing contact bet-Ween the shoulders 43 and 54 remains and there is no relative movement between the upper end portion 44 of the mandrel and the body. Thus, the only seal which is required between moving parts is that shown as 82. This is a balanced low pressure seal, however, since the pressure of the fluid exerted upwardly on the seal is balanced by the pressure of fluid on the upper end thereof admitted through port 83. As discussed hereinbefore the magnitude of relative movement between the portion of the mandrel to which the bit is attached and the body is exemplified by movement `of less than one inch under a load of 100,000 pounds. Shock and vibration are damped out by transmission through lthe isolating member 60 since all forces transmitted upwardly or downwardly through the cushion drill collar must pass through the member 60. The isolating member thus comprises a cylinder of resilient material interposed in the drill string.

Thus, the present invention provides an improved drill collar shock absorber which is simple and effi-cient in construction and operation and which obviates maintenance and sealing problems by eliminating the necessity of moving parts at high pressure sealed areas.

What is claimed is:

1. A drill collar shock absorber adapted to be inserted into a drilling string comprising:

a body portion adapted to be connected to the drill string extending upwardly therefrom;

a mandrel adapted to be connected to the portion of the drill string extending downwardly therefrom;

an isolating member of resilient dimensionally stable material longitudinally interposed between and separating longitudinal portions of said mandrel, said isolating member forming a Wall of said mandrel; and

means non-rotatably connecting said body and said mandrel.

2. A drill collar shock absorber adapted to be inserted into a drilling string comprising:

a body defining a longitudinally extending opening therein and an inwardly extending transverse downwardly facing shoulder;

a mandrel matable with said body in said opening in bearing contact with said shoulder;

a cylindrical resilient isolating member, said member being interposed in said mandrel to form the entire cross-section thereof along a longitudinally extending portion of said mandrel; and

means non-rotatably connecting said body and said mandrel.

3. A drill collar shock absorber comprising:

a body having an upper end adapted to be engaged with a drill string extending upwardly therefrom, said body having a longitudinal opening of first diameter extending from the upper end thereof and an opening of second diameter extending from the lower end thereof, said second diameter being substantially greater than said first diameter and defining an inwardly extending transverse shoulder in the inner wall of said body;

a mandrel having a lower end adapted to be connected to a portion of a drill string extending downwardly therefrom, said mandrel having a transverse surface in bearing contact with said shoulder, said mandrel being slidably longitudinally engaged in said opening of second diameter;

a resilient isolating member, said isolating member being tubular in configuration with an inside diameter approximately equal to said first diameter and an outside diameter approximately equal to but less than said second diameter, said isolating member being interposed in said mandrel to form the inner and outer walls thereof along a longitudinal portion thereof within said mandrel;

means lfor retaining said mandrel and body in assembled condition; and,

means for nonarotatably interconnecting said mandrel and body, whereby all longitudinal forces transmitted through said shock absorber pass through said isolating member which lengthens and foreshortens in response to shock and vibration while retaining relatively non-movable contact between the upper end of said mandrel and the wall of said body.

4. A drill collar shock absorber comprising:

a body having an upper end adapted to be engaged with a drill string extending upwardly therefrom, said body having a longitudinal opening of first diameter extending from the upper end thereof and an opening of second diameter extending from the lower end thereof, said second diameter being substantially greater than said first diameter and defining an inwardly extending transverse shoulder in the inner wall of said body;

a mandrel having a lower end adapted to be connected to a portion of 1a drill string extending downwardly therefrom, said mand-rel having a transverse surface in bearing contact with said shoulder, said mandrel being slidably longitudinally engaged in said opening of second diameter;

a resilient isolating member, said isolating member being tubular in configuration with an inside diameter approximately equal to said first diameter and an outside diameter approximately equal to but less than said second diameter, said isolating member being interposed in said mandrel to form the inner and outer walls thereof along a longitudinal portion thereof within said mandrel;

means for retaining said mandrel and body in assembled condition; and,

liuid sealing means between said body and mandrel proximate the upper end of said mandrel, whereby all longitudinal forces transmitted through said shock absorber pass through said isolating member which lengthens and foreshortens in response to shock and vibration while retaining relatively non-movable contact between the upper end ofsaid mandrel and the wall of said body.

5. A drill collar shock absorber comprising:

a body having an upper end adapted to be engaged with a drill string extending upwardly therefrom, saidy body having a longitudinal opening of first diameter extending from the upper end thereof and an opening of second diameter extending from the lower end thereof, said second diameter being substantially greater than said first diameter and defining an ina mandrel having a lower end adapted to be connected to a portion of a drill string extending downwardly thereof within said mandrel;

means for retaining said mandrel and body in assembled condition; and

a mandrel having a lower end adapted to be connected to a portion of a drill string extending downwardly therefrom, said mandrel having a transverse surface in bearing contact with said shoulder, said mandrel therefrom, said mandrel having a transverse surface being slidably longitudinally engaged in said opening in bearing contact with said shoulder, said mandrel of second diameter;

being slidably longitudinally engaged in said opening resilient isolating member, said isolating member of second diameter; being tubular in configuration with an inside diama resilient isolating member, said isolating member eter approximately equal to said rst diameter and being tubular in conguration with an inside diam- 10 an outside diameter approximately equal to but less eter approximately equal to said rst diameter and than said second diameter, said isolating member anoutside diameter approximately equal to but less being interposed in said mandrel to form the inner than said second diameter, said isolating member and outer walls thereof along a longitudinal portion being interposed in said mandrel to form the inner thereof within said mandrel;

and outer walls thereof along a longitudinal portion means for `retaining said mandrel and body in assembled condition; and

said isolating member being formed of polymerized formaldehyde resin, whereby all longitudinal forces said isolating member being formed of resilient dimensionally stable plastic material, whereby all longi 20 tudinal forces transmitted through said shock absorber pass through said isolating member which lengthens and foreshortens in response to shock and transmitted through said shock absorber pass through said isolating member which lengthens and foreshortens in response to shock and vibration while Iretaining relatively non-movable contact between the upper end of said mandrel and the Wall of said Vibration while retaining relatively non-movable body, contact between the upper end of said mandrel and References Cited the wall of said body.

6. A drill collar shock absorber comprising: UNITED STATES PATENTS a body having an upper end adapted to be engaged with 2,756,022 7 195 6 Sturgeon 64-23 a drill string extending upwardly therefrom, said body 2,795,398 6/ 1957 Ragland 64-11 having a longitudinal opening of first diameter ex- 2,987,129 6/1961 Webb. tending from the upper end thereof and an opening 2,991,635 7/ 1961 Warren 64-23 of second diameter extending from the lower end thereof, said second diameter being substantially greater than said first diameter and dening an inwardly extending transverse shoulder in the inner HALL C. COE, Examiner. wall of said body;

FRED C. MATTERN, J R., Primary Examiner. 

2. A DRILL COLLAR SHOCK ABSORBER ADAPTED TO BE INSERTED INTO A DRILLING STRING COMPRISING: A BODY DEFINING A LONGITUDINALLY EXTENDING OPENING THEREIN AND AN INWARDLY EXTENDING TRANSVERSE DOWNWARDLY FACING SHOULDER; A MANDREL MATABLE WITH SAID BODY IN SAID OPENING IN BEARING CONTACT WITH SAID SHOULDER; A CYLINDRICAL RESILIENT ISOLATING MEMBER, SAID MEMBER BEING INTERPOSED IN SAID MANDREL TO FORM THE ENTIRE CROSS-SECTION THEREOF ALONG A LONGITUDINALLY EXTENDING PORTION OF SAID MANDREL; AND MEANS NON-ROTATABLY CONNECTING SAID BODY AND SAID MANDREL. 